The present invention relates to a signal swing trimming apparatus and method, and more particularly, to a high-speed USB output swing trimming apparatus and method.
The universal serial bus (USB) interface is one of the most common interface standards of digital wired communications. Originally released in 1995 at 12 Mbps, USB today operates at 480 Mbps and can be found in many kinds of electrical devices. Due to the advantages of a high transmission rate and the ability to plug-and-play, there is a trend to equip products with standard USB interfaces. Some of the common applications are digital cameras, external USB flash cards, and external hard disks.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a USB system 100 of prior art. The USB system 100 comprises of an USB device 102 coupled to a USB host 104. According to prior art, the data transfer between the USB device 102 and the USB host 104 is configured as a differential signal DP, DM. Thus, the input impedance of each terminal in the USB device 102 is set to 45Ω. Due to the fabricating process or other reasons, however, the input impedance of the USB device 102 may not be perfectly matched to 45Ω, which resulting in a swing of the differential signal DP, DM that may vary outside of the USB specification. Therefore, the compatibility problem that arises from the impedance mismatching between the USB device 102 and the USB host 104 is one of the most critical problems in the field of high-speed USB systems.